It is known that furfuryl alcohol can be converted into levulinic acid or alkyl levulinate by reacting furfuryl alcohol and water or an alkyl alcohol in the presence of a homogeneous strong acidic catalyst. In U.S. Pat. No. 4,236,021, for example, is disclosed the esterification of furfuryl alcohol with a different alcohol in the presence of a strong acid catalyst such as hydrogen chloride, hydrogen bromide or oxalic acid. In U.S. Pat. No. 5,175,358 is disclosed the production of levulinic acid by heating and ring-opening furfuryl alcohol in the presence of water and a strong non-oxidising protonic acid, wherein the furfuryl alcohol is progressively introduced into a mixture of water, the strong protonic acid and an amount of levulinic acid that serves as the reaction solvent. Hydrochloric acid, hydrobromic acid, hydroiodic acid, sulphuric acid, pyrosulphuric acid, perchloric acid, the phenylsulphonic acids, methanesulphonic acid, chlorosulphonic acid and fluorosulphonic acid are mentioned as being exemplary of such strong protonic acids.
In U.S. Pat. No. 2,738,367 is disclosed a process for producing levulinic acid by heating an aqueous solution of furfuryl alcohol at a temperature in the range of from 30 to 100° C. in the presence of a strongly acidic exchange resin as catalyst. The catalysts that are disclosed in U.S. Pat. No. 2,738,367, i.e. the cation exchange resins marketed under the tradenames “Amberlite IR-120” and “Amberlite IR-105”, are both gel-type cation exchange resins, i.e. a non-porous form of cation exchange resin.